I ate my wafer...

4/02/2007

Blank firing guns

James has pointedly requested a technical description of the various methods that are used to make blank cartridges cycle through semi-automatic and automatic firearms (and non-gun replicas). So, Here's the short version:

A. The non-guns that are capable of firing blanks typically have a very light breachblock, blowback mechanism, sometimes with a restricted bore to increase operating pressure. Usually, these guns are diecast from a light weight alloy such as Zamak, so the mechanism has the same outward appearance as the real version, but is light (and therefore easy to operate with blanks as per Newtonian physics). The obvious question is how a mechanism that is intended to work as a locked breach pistol for hot 9x19mm loads can be adapted, even as a diecast non-gun to run light impulse blanks. The answer is that usually the mechanism is adapted remove locking features, and the best simple example I know is the way that Glock adapts the G19 design to .380 ACP by removing the locking shoulder on the barrel. Additionally, to run blanks, a barrel restriction is usually needed to increase operating pressure (see below).

B. There are some non-guns that simply ignite flammable gases like propane to simulate firing. This approach is common to fake belt-fed machine guns used for reenacting. In essence, this method is sort of like a very special projectile-less potato gun that ignites fresh charges of fuel and oxygen multiple times in quick succession making flames and noise without having to use the explosion to work a mechanism.

C. Finally, regular semi-auto and full auto small arms can be adapted to function with blanks by simply adding a carefully engineered restriction to the bore. Within reason, it doesn’t matter whether a weapon is originally blowback, recoil, or gas operated, a restricted bore will allow function with blanks. To simplify, adding a restriction to the bore causes the gas from the blank to push backwards on the cartridge, and to pressurize the gas mechanism (on gas operated weapons) enough to cause forces as strong as incurred in firing live ammo. How much restriction is needed depends on the particular weapon’s requirements, the blank cartridge (how much gas is produced, and how quickly), and environmental concerns (what altitude/temperature).

D. Often, military weapons are adapted for training purposes by a plate temporarily attached to the muzzle, known in the U.S. as a blank firing adaptor. Now, most military blank adaptors are conspicuous when on the weapon for safety reasons, and reenactors prefer original appearing weapons. So, in an act of sacrilege, it is common to drill and tap the muzzle of full and semi-auto weapons to take a removable setscrew (which is predrilled with a small hole to allow some gas to escape). After a rifle or machinegun is mutilated by installing a setscrew it may shoot ball ammunition somewhat accurately with the setscrew is removed, but I wouldn’t recommend modifying a rare rifle (say a gas trap M1) then talking about it around serious collectors or shooters.

E. Non-repeating guns like bolt action rifles and muzzle loaders can shoot blank ammo without modification, since they do not need to tap energy the act of firing. For historical context, at Lexington, several members of the milita thought that the Birtish were firing blanks, and until they saw hits from musket balls, could not tell the difference between blank and ball loads (read the HIGHLY reccomended "Paul Revere's Ride" by David Hackett Ficscher for examples) .